Sliding part and method of manufacturing the same

ABSTRACT

There is provided a sliding part in which a surface coverage ratio of copper in the sliding part increases. A bearing which is the sliding part is formed by filling the raw powder into the filling portion of the forming mold, compacting the raw powder to form a powder compact, which is sintered. A copper-based raw powder is composed of a copper-based flat raw powder whose diameter is smaller than that of an iron-based raw powder and an aspect ratio larger than that of the iron-based raw powder, and a copper-based small-sized raw powder whose diameter is smaller than that of the copper-based flat raw powder. The copper is allowed to segregate at the surface of the sliding part. The surface of the bearing is covered with the copper-based small-sized raw powder and the copper-based flat raw powder, thereby the surface coverage ratio of copper can be increased.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application is a Divisional of U.S. patent application Ser. No.11/911,842, filed Oct. 18, 2007, now abandoned, which is a U.S. NationalPhase application under 35 U.S.C. §371 of International PatentApplication No. PCT/US2005/020802, filed Nov. 14, 2005, which claims thebenefit of Japanese Patent Application No. 2005-123009, filed Apr. 20,2005, all of which are incorporated by reference herein. TheInternational Application was published in Japanese on Nov. 2, 2006 asInternational Publication No. WO 2006/114911 under PCT Article 21(2).

FIELD OF THE INVENTION

The present invention relates to a sliding part such as a bearing or thelike and a method of manufacturing the same.

BACKGROUND OF THE INVENTION

As a sliding part having reduced frictional resistance and improveddurability and generating no noise, a sliding part is known that is aflat powder formed by sintering a powder compact, which is fabricated byfilling an iron-based raw powder and a copper-based raw powder in afilling portion of a forming mold and applying vibration to the mold atthe same time for compacting, and having an aspect ratio of thecopper-based raw powder larger than that of the iron-based raw powder,on a surface of which copper segregates (for example, refer to JapaneseUnexamined Patent Application, First Publication No. 2003-221606); or asliding part that is a flat powder formed by sintering a powder compact,which is fabricated by filling the iron-based raw powder and thecopper-based raw powder into the filling portion of the forming mold andapplying vibration to the mold at the same time for compacting, andhaving an average value of a maximum projected area of the copper-basedraw powder larger than that of the iron-based raw powder, in which thecopper-base raw powder contains flat powder of copper or copper-alloyand on a surface of which copper segregates (for example, refer toJapanese Unexamined Patent Application, First Publication No.2004-84038).

SUMMARY OF INVENTION Problems to be Solved by the Invention

However, in the above related art, the mixture of the iron-based rawpowder and the copper-based flat raw powder composed of flat powderhaving a larger aspect ratio than the iron-based raw powder is filledinto the filling portion of the forming mold, and at the same timevibration is applied to the forming mold, such that the copper-basedflat raw powder segregates at the outer side within the filling portion,overlaps each other in the thickness direction, and at the same timesegregates at a gathering surface in a state in which the directionintersecting the thickness direction is aligned with the longitudinaldirection of the surface. However, the iron-based raw powder emerges ata part of the surface, as well as the segregated copper-based flat rawpowder, and a gap is formed between the copper-based flat raw powderswhich emerges at the surface and are adjacent to each other. As aresult, the gap between the copper-based raw powder and the iron-basedraw powder, or the gap between the copper-based flat raw powders isformed in the surface. Due to these gaps, the surface coverage ratio ofthe copper in the sliding part cannot be increased.

Accordingly, it is an advantage of the present invention to increase thesurface coverage ratio of the copper in the sliding part formed byfilling the iron-based raw powder and the copper-based raw powder havingan aspect ratio larger than that of the iron-based raw powder into thefilling portion of the forming mold, compacting the raw powders to forma powder compact, and sintering the powder compact, in which the coppersegregates at the surface of the sliding part.

Means for Solving the Problem

According to a first aspect of the invention, a sliding part is formedby filling an iron-based raw powder and a copper-based raw powder into afilling portion of a forming mold, compacting the raw powders to form apowder compact, and sintering the powder compact. The copper-based rawpowder is composed of a copper-based flat raw powder having an averagediameter smaller than that of the iron-based raw powder and an aspectratio larger than that of the iron-based raw powder; and a copper-basedsmall-sized raw powder having the average diameter smaller than that ofthe copper-based flat raw powder; and in which copper is allowed tosegregate on a surface of the sliding part.

According to a second aspect of the invention, in the sliding partaccording to the first aspect, the surface coverage ratio of copper inthe sliding part is 80% or more.

According to a third aspect of the invention, in the sliding partaccording to the first or second aspect, the aspect ratio of thecopper-based flat raw powder is 10 or more.

According to a fourth aspect of the invention, in the sliding partaccording to the second aspect, the ratio of the copper-based raw powderis 20 to 40% by weight with respect to all raw powders.

According to a fifth aspect of the invention, a sliding part is formedby filling an iron-based raw powder and a copper-based raw powder into afilling portion of a forming mold, compacting the raw powders to form apowder compact, and sintering the powder compact. The copper-based rawpowder consists of a copper-based flat raw powder having an averagevalue of a maximum projected area smaller than that of the maximumprojected area of the iron-based raw powder and an aspect ratio largerthan that of the iron-based raw powder; and a copper-based small-sizedraw powder having the average value of the maximum projected areasmaller than that of the maximum projected area of the copper-based flatraw powder; and in which copper is allowed to segregate on a surface ofthe sliding part.

According to a sixth aspect of the invention, in the sliding partaccording to the fifth aspect, a surface coverage ratio of copper in thesliding part is 80% or more.

According to a seventh aspect of the invention, a method ofmanufacturing a sliding part, includes steps of filling an iron-basedraw powder and a copper-based raw powder into a filling portion of aforming mold, compacting the raw powders to form a powder compact, andsintering the powder compact, in which the copper-based raw powderconsists of a copper-based flat raw powder having the average diametersmaller than that of the iron-based raw powder and an aspect ratiolarger than that of the iron-based raw powder; and a copper-basedsmall-sized raw powder having an average diameter smaller than that ofthe copper-based flat raw powder; and the copper-based flat raw powderin the filling portion is allowed to segregate on a surface of thepowder compact.

According to an eighth aspect of the present invention, a method ofmanufacturing a sliding part, includes steps of filling an iron-basedraw powder and a copper-based raw powder into a filling portion of aforming mold, compacting the raw powders to form a powder compact, andsintering the powder compact, in which the copper-based raw powder iscomposed of a copper-based flat raw powder having an average value ofthe maximum projected area smaller than that of the maximum projectedarea of the iron-based raw powder and an aspect ratio larger than thatof the iron-based raw powder; and a copper-based small-sized raw powderhaving an average value of the maximum projected area smaller than thatof the maximum projected area of the copper-based flat raw powder, inwhich the copper-based flat raw powder in the filling portion is allowedto segregate on a surface of the powder compact.

According to a ninth aspect of the invention, in the method ofmanufacturing the sliding part according to the seventh or eighthaspect, the aspect ratio of the copper-based flat raw powder is 10 ormore.

According to a tenth aspect of the invention, in the method ofmanufacturing the sliding part according to any one of the seventh toninth aspects, a ratio of the copper-based raw powder is 20 to 40% byweight with respect to all raw powders.

Effects of the Invention

According to the first and fifth aspects of the present invention, whena bearing is composed of the sliding part, the copper-based small-sizedraw powder as well as the copper-based flat raw powder emerges at thesurface, such that a rotator slides on the surface covered with thecopper, and the coefficient of the friction between the rotation axisand the surface side decreases, thus a rotation is performed smoothly.At the same time, predetermined strength and durability can be obtaineddue to the iron. Furthermore, in the above structure, even though thesurface on which the rotator rotates is abraded, since the predeterminedratio of copper is contained below the surface, the durability of thesliding portion becomes excellent.

According to the second and sixth aspects of the present invention, thecoefficient of the friction of the sliding portion can be suppressed ata significantly lower level.

According to the third and ninth aspects of the present invention, sincethe aspect ratio is set to 10 or more, when vibration is applied, theflat powder segregates easily at the surface, and thus it is possible toobtain the sliding part having a high copper concentration at thesurface.

According to the fourth aspect of the present invention, when the ratioof the copper-based flat raw powder is less than 20% by weight, theratio of copper at the surface decreases and the frictional resistanceincreases. In addition, when the ratio of copper-based flat raw powderexceeds 40% by weight, the ratio of the copper-based raw powder in allof the raw powders becomes too large, and it is not favorable in termsof the strength. Therefore, if the ratio is set in the range of 20 to40%, the frictional resistance decreases and it is possible to obtain asliding part having a high strength.

According to the seventh and eighth aspects of the present invention, itis possible to obtain a sliding part having a low coefficient offriction and an improved durability.

According to the tenth aspect of the present invention, when the ratioof the copper-based flat raw powder is less than 20% by weight, theratio of copper at the surface decreases and the frictional resistanceincreases. In addition, when the ratio of the copper-based flat rawpowder exceeds 40% by weight, the ratio thereof becomes too large and itis not favorable in terms of the strength. Therefore, if the ratio isset in the range of 20% to 40% by weight, the frictional resistancedecreases and it is possible to obtain a sliding part having a highstrength.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart illustrating a manufacturing method according to afirst embodiment of the present invention.

FIG. 2 is a schematic front elevation view of an iron-based raw powderaccording to the first embodiment of the present invention.

FIG. 3(A) is a schematic side elevation view illustrating a copper-basedraw powder according to the first embodiment of the present invention.

FIG. 3(B) is a schematic front elevation view illustrating acopper-based raw powder according to the first embodiment of the presentinvention.

FIG. 4 is a schematic front elevation view of a copper-based small-sizedraw powder according to the first embodiment of the present invention.

FIG. 5 is a perspective view illustrating a bearing according to thefirst embodiment of the present invention.

FIG. 6 is a sectional view illustrating a forming mold according to thefirst embodiment of the present invention.

FIG. 7 is a schematic sectional view illustrating a powder compactaccording to the first embodiment of the present invention, in which aportion of the powder compact is enlarged.

BRIEF DESCRIPTION OF THE REFERENCE SYMBOLS

-   -   1: iron-based raw powder    -   2: copper-based flat raw powder    -   3: copper-based small-sized raw powder    -   5: bearing    -   6: powder compact    -   11: forming mold    -   16: filling portion    -   51: sliding surface (sliding part)

DETAILED DESCRIPTION OF THE INVENTION Best Mode for Carrying Out theInvention

Hereinafter, a preferred embodiment of the present invention will bedescribed with reference to the attached drawings. However, theembodiment to be described below is not intended to limit the inventiondescribed in claims. Furthermore, the entire constitutions to bedescribed later are not essential to the invention.

Embodiment 1

A method of manufacturing the invention will now be described. Aniron-based raw powder 1, a copper-based flat raw powder 2, and acopper-based small-sized raw powder 3 are mixed at a predetermined ratio(S1). As shown in FIG. 2, as the iron-based raw powder 1, anirregular-shaped powder having a substantially spherical shape such asan atomized powder is used. An average diameter of the iron-based rawpowder 1 is in the range of 50 to 100 μm, but is preferably in the rangeof 60 to 80 μm. Furthermore, as shown in FIG. 3, a flat powder is usedas the copper-based raw material 2. An aspect ratio (diameterD/thickness T) of the flat powder is 10% or more, but is preferably inthe range of 20 to 50%. The average diameter D of the copper-based flatraw powder 2 is 80 μm, and the average thickness T is in the range of 1to 5 μm. Furthermore, as the copper-based flat raw powder 2, it ispossible to use a mixture consisting of a copper powder as the maincomponent and a tin powder in the range of 2 to 30% by weight.Furthermore, as shown in FIG. 4, an irregular-shaped powder having asubstantially spherical shape is used as the copper-based small-sizedraw powder 3. The average diameter of the copper-based small-sized rawpowder 3 is in the range of 30 to 50 μm, but is preferably 20 μm.

Herewith, the average diameter of the copper-based flat raw powder 2becomes smaller than that of the iron-based raw powder 1, and becomeslarger than that of the copper-based small-sized raw powder 3. Due tothe above comparative difference in size, the average value of themaximum projected area A of the copper-based flat raw powder 2 becomessmaller than that of the maximum value of the projected area B of theiron-based raw powder 1, and the average value of the maximum projectedarea A becomes larger than that of the maximum projected area C of thecopper-based small-sized raw powder 3.

As shown in FIG. 5, a bearing 5 has a substantially cylindrical shapeand a substantially cylindrical-shaped sliding surface 51, on which arotational shaft, which is a rotator (not shown), rotationally slides,is formed at the center of the bearing 5. At both sides in thelongitudinal direction of the sliding surface 51, which is a slidingportion, flat end surfaces 52 and 53 are formed, and an outercircumferential surface 54 thereof is formed like a cylindrical shape.

The mixture (mixed at S1) of the iron-based raw powder 1, thecopper-based flat raw powder 2, and the copper-based small-sized rawpowder 3 is filled into a filling portion 16 of a forming mold 11. Inthe mixed powder filled into the filling portion 16, a ratio of thecopper-based flat raw powder is 20 to 40% by weight with respect to allraw powders.

FIG. 6 is an example of the forming mold 11. The forming mold 11includes a die 12, a core rod 13, a lower-side punch 14, and anupper-side punch 15. A vertical direction of the forming mold 11 is anaxial direction (a vertical axial direction of the press). The die 12has a substantially cylindrical shape, and the core rod 13 having asubstantially cylindrical shape is coaxially positioned in the die 12.The lower-side punch 14 has a substantially cylindrical shape and isfitted between the die 12 and the core rod 13 from the lower side, sothat the lower-side punch 14 can move in the vertical direction. Theupper punch 15 has a substantially cylindrical shape and is fittedbetween the die 12 and the core rod 13 from the upper side, so that theupper-side punch 15 can move in the vertical direction and in such amanner as to be freely detachable. Furthermore, the filling portion 16is formed among the die 12, the core rod 13, and the lower-side punch14. An inner circumferential surface of the die 12 forms the outercircumferential surface 54. An upper surface of the lower-side punch 14forms the end surface 53. A lower surface of the upper-side punch 15forms the end surface 52. The outer circumferential surface of the corerod 13 forms the sliding surface 51.

As shown in FIG. 6, the mixture of the iron-based raw powder 1, thecopper-based flat raw powder 2, and the copper-based small-sized rawpowder 3 is filled into the filling portion 16, and a vibration isapplied to the mixture of the raw materials 1 to 3 (S2). In this case,the upper side of the filling portion 16 is closed by the upper-sidepunch 15, and vibration is applied to the filling portion 16 at theaccelerating speed of 0.01 to 3G without pressing the punches 14 and 15.When the vibration is applied to the filling portion 16, thecopper-based flat raw powder 2, which is flat powder, segregates at theouter side within the filling portion 16, that is, at the slidingsurface 51 or the outer circumferential surface 54, overlaps each otherin the thickness direction, and gathers so as to make the directionintersecting the thickness direction aligned with the longitudinaldirection of the surface. In addition, the iron-based raw powder 1sometimes emerges between the copper-based flat raw powders 2 as well asthe segregated copper-based flat raw powder 2 in the outer side withinthe filling portion 16. However, the copper-based small-sized raw powder3A intrudes into the gap formed between the iron-based raw powder 1 andthe copper-based flat raw powder 2 and then emerges at the outer side,or the copper-based small-sized raw powder 3B intrudes into the gapformed between the copper-based flat raw powders 2 and then emerges atthe outer side. As a result, the surface coverage ratio of copper in thesliding surface 51 becomes 80% or more, or 85% or more. The surfacecoverage ratio of copper means the surface coverage ratio not includingthe hole region, like the surface coverage ratio of copper in the latterrelated art.

Furthermore, since the flat surface of the copper-based raw powder 2 iswide, it is possible to segregate the copper-based raw powder 2 at theouter side within the filling portion 16 by generating staticelectricity on the surface of the forming mold 11 surrounding thefilling portion 16, or it is possible to segregate the copper-based rawpowder 2 at the outer side within the filling portion 16 by usingmagnetic force as well as the vibration.

On the other hand, the remaining copper-based flat raw powder 2A at theinner side that has not segregated at the outer side within the fillingportion 16, that is, the sliding surface 51 and the outercircumferential surface 54 are disposed to surround the iron-based rawpowder 1 with the plurality of copper-based small-sized raw powders 3.

Then, the upper-side and lower-side punches 15 and 14 press the mixtureof the raw powders 1 to 3 within the filling portion 16 to form a powdercompact 6 (S3). As shown in FIG. 7, the copper-based flat raw powder 2,which is a flat powder, emerges at the surface, and the ratio of theiron-based raw powder 1 increases as it goes toward the inner side ofthe powder compact 6. The powder compact 6 is sintered (S4) to form asintered bearing 5. A post process such as a sizing process or an oilimpregnation process is performed on the bearing 5, if needed.

In the above embodiment, in accordance with the first aspect, in thebearing 5 which is a sliding part formed by filling the raw powder intothe filling portion 16 of the forming mold 11, compacting the raw powderto form a powder compact 6, and sintering the powder compact 6, thecopper-based raw powder is composed of the copper-based flat raw powder2 having an average diameter smaller than that of the iron-based rawpowder 1 and an aspect ratio larger than that of the iron-based rawpowder 1; and the copper-based small-sized raw powder 3 having anaverage diameter smaller than that of the copper-based flat raw powder2, and the copper is allowed to segregate at the surface of the slidingpart. Therefore, the copper-based raw powder 2, which is a flat powder,and the iron-based raw powder 1 are filled into the filling portion 16,and the vibration is applied thereto, such that the copper-based flatpowder segregates at the surface. Furthermore, in the obtained bearing5, the surface is covered with the copper-based small-sized raw powder 3emerged on the surface as well as the copper-based flat raw powder 2,thereby it is possible to increase the surface coverage ratio of copper.

Therefore, the rotator slides on the sliding surface 51 which is coveredwith the copper, and the coefficient of friction between the rotationaxis and the sliding surface 51 becomes small, thereby the rotationperforms smoothly. In addition, the predetermined strength and thedurability can be obtained due to the iron. Furthermore, in the abovestructure, even though the sliding surface 51, on which the rotatorrotates, is abraded, since a predetermined ratio of copper is containedbelow the sliding surface 51, the durability of the sliding portionbecomes excellent.

Furthermore, in the above embodiment, in accordance with the second andsixth aspects, since the surface coverage ratio of copper in the slidingsurface 51, which is the sliding portion, is 80% or more, it is possibleto suppress the coefficient of the friction at a significantly lowerlevel.

Furthermore, in the above embodiment, in accordance with the third andninth aspects, since the aspect ratio of the copper-based flat rawpowder 2 is set to 10 or more, when a vibration is applied, thecopper-based flat powder 2 segregates easily at the surface, and it ispossible to obtain the bearing 5 having a high copper concentration atthe surface.

Furthermore, in the above embodiment, in accordance with the fourthaspect, since the ratio of the copper-based flat raw powder 2 is set inthe range of 20% to 40%, it is possible to obtain a bearing 5 having lowfrictional resistance and high strength.

Furthermore, in the above embodiment, in accordance with the fifthaspect, in the bearing 5 formed by filling the raw powder into thefilling portion 16 of the forming mold 11, compacting the raw powder toform the powder compact 6, and sintering the powder compact 6, thecopper-based raw powder is composed of the copper-based flat raw powder2 having an average value of the maximum projected area A smaller thanthe average value of the maximum projected area B of the iron-based rawpowder 1 and an aspect ratio larger than that of the iron-based rawpowder 1; and the copper-based small-sized raw powder 3 having theaverage value of the maximum projected area C smaller than that of themaximum projected area A of the copper-based flat raw powder 2, and thecopper is allowed to segregate at the surface of the sliding part.Therefore, the copper-based raw powder 2, which is a flat powder, andthe iron-based raw powder 1 are filled into the filling portion 16, andthe vibration is applied thereto, such that the copper-based flat powdersegregates at the surface. Furthermore, in the obtained bearing 5, thesurface is covered with the copper-based small-sized raw powder 3 thathas emerged on the surface as well as the copper-based flat raw powder2, thereby it is possible to increase the surface coverage ratio ofcopper.

Furthermore, in the above embodiment, in accordance with the seventh andeighth aspects, the surface is covered with the copper-based small-sizedraw powder 3 that has emerged at the surface as well as the copper-basedflat raw powder 2 appear, it is possible to obtain the bearing 5, thesurface coverage ratio of copper of which increases.

Furthermore, in the above embodiment, in accordance with the tenthaspect, since the ratio of the copper-based raw powder is set in therange of 20% to 40% by weight with respect to all of the raw powders,the frictional resistance decreases and it is possible to obtain thesliding part having a high strength.

Furthermore, the present invention is not limited to the aboveembodiment, and various modifications can be made. For example, the flatpowder can include a rod-shaped powder. In this case, the ratio of thelength and the diameter becomes the aspect ratio.

INDUSTRIAL APPLICABILITY

The above sliding part and the method of manufacturing the sameaccording to the aspects of the invention can be applied to varioussliding parts in addition to the bearing.

What is claimed is:
 1. A method of manufacturing a sliding partcomprising: filling an iron-based raw powder and a copper-based rawpowder into a filling portion of a forming mold; vibrating the fillingportion of the forming mold at the accelerating speed of between 0.01 to3G, wherein the powders filing the forming mold are uncompressed;compacting the raw powders to form a powder compact; and sintering thepowder compact, wherein the copper-based raw powder is comprised of acopper-based flat raw powder having an average diameter smaller thanthat of the iron-based raw powder and an aspect ratio larger than thatof the iron-based raw powder; and a copper-based small-sized raw powderhaving an average diameter smaller than that of the copper-based flatraw powder, and wherein part of the copper-based flat raw powders issegregated on the outer side within the filling portion by applying thevibration, and the grains of the copper-based small raw powder intrudeinto spaces formed between the grains of the iron-based raw powder tosurround the grains of the iron-based raw powder by applying thevibration.
 2. The method according to claim 1, wherein the aspect ratioof the copper-based flat raw powder is 10 or more.
 3. The methodaccording to claim 1, wherein a ratio of the copper-based raw powder is20 to 40% by weight with respect to all raw powders.
 4. A method ofmanufacturing a sliding part comprising: filling an iron-based rawpowder and a copper-based raw powder into a filling portion of a formingmold; vibrating the filling portion of the forming mold at theaccelerating speed of between 0.01 to 3G wherein the powders filing theforming mold are uncompressed; compacting the raw powders to form apowder compact; and sintering the powder compact, wherein thecopper-based raw powder is comprised of a copper-based flat raw powderhaving an average value of a maximum projected area smaller than that ofthe maximum projected area of the iron-based raw powder and an aspectratio larger than that of the iron-based raw powder; and a copper-basedsmall-sized raw powder having an average value of a maximum projectedarea smaller than that of the maximum projected area of the copper-basedflat raw powder, and wherein part of the copper-based flat raw powdersis segregated on the outer side within the filling portion by applyingthe vibration, and the grains of the copper-based small raw powderintrude into spaces formed between the grains of the iron-based rawpowder to surround the grains of the iron-based raw powder by applyingthe vibration.
 5. The method according to claim 4, wherein the aspectratio of the copper-based flat raw powder is 10 or more.
 6. The methodaccording to claim 4, wherein a ratio of the copper-based raw powder is20 to 40% by weight with respect to all raw powders.
 7. The methodaccording to claim 2, wherein a ratio of the copper-based raw powder is20 to 40% by weight with respect to all raw powders.